Your Thoughts on Black Hole Production at CERN

I'm interested in hearing from the experts (practicing physicists and teachers) here about what you think of the possibility of an artificial black hole being created at CERN and, specifically, if you think it possible the black hole could interact with surrounding matter and pose a danger to the Earth.

The arguments against this seem to be:

1) If string theory is right and black holes can be formed in a high energy collider, then Hawking radiation is also right and the black hole will evaporate before it can interact with a single piece of matter.

2) If black hole production were even possible, then the high energy cosmic rays would have done so already.

While I don't consider myself an alarmist, I do wish scientists had a slightly better idea of what might happen than a bunch of "if ... then"'s. In the 1940s, some believed the atomic bomb would ignite the atmosphere; this possibliity, however, was mathematically disproven early on. In the case of black hole production, the lack of certainty on anyone's part as to what might happen seems, to me, a little disconcerting.

Perhaps the reason there are no alien civilizations communicating with us is that they all destroyed themselves with particle accelerators before they had a chance. :)

I don't understand why you think a calculation of the atmosphere ignition conditions is acceptable but a calculation of Hawking radiation is not.

I also don't understand why you don't accept the cosmic ray argument. Nothing is happening at the LHC that isn't happening in the upper atmosphere, except that there's a detector to monitor what's happening.

Finally, to get an earth-destroying black hole, you need different production properties, different decay properties, different production kinematics and most likely different gravitational properties than a black hole. I would argue that black hole is a poor name for an object that shares no properties with what most people call black holes. So the question really is "how do you know that you won't produce some new unpredicted thing that destroys the world, but didn't happen the last zillion times the same initial conditions were produced."

The answer is, technically, we don't know that just because it didn't happen the last N times it won't happen on try number N+1. Pushing N reindeer off a roof doesn't prove that reindeer can't fly - it just proves that these reindeer can't (or won't) fly. However, how do we know that drinking a glass of water won't end the universe, just because the last trillion glasses of water didn't? It's the same argument, only the glass of water one is less well tested.

I don't understand why you think a calculation of the atmosphere ignition conditions is acceptable but a calculation of Hawking radiation is not.

Because combustion was a well understood concept in 1944. Hawking radiation has never even been directly observed.

I also don't understand why you don't accept the cosmic ray argument. Nothing is happening at the LHC that isn't happening in the upper atmosphere, except that there's a detector to monitor what's happening.

My understanding is that the micro black holes are not moving very fast w/r/t the Earth. Cosmic rays would produce relativistic black holes which would zip through the earth and out the other side, if any. These micro black holes MIGHT have a chance to stick around to do damage.

Finally, to get an earth-destroying black hole, you need different production properties, different decay properties, different production kinematics and most likely different gravitational properties than a black hole.

Great question peter!
The threat of a black hole being created in the LHC is ridiculous - not to put too fine of a point on it.
There is a possibility that a black hole would be created in the LHC. A very very very unfortunately small possibility -> if it does produce them, that will be great!

Black-hole evaporation is quite likely; i think you're right that it hasn't been observed - so it most certainly isn't confirmed in any way, but its even fairly well agreed upon in the astrophysics community (which is saying alot). Even if not by hawking radiation; a black-hole would possibly be destroyed by other means, for instance: non-virtual particle based anti-matter annihilation and tunneling evaporation (much less likely).

As previously said, the atmosphere experiences similar high energy/density situations - which hasn't resulted in any trouble. The speed of the supposed black-hole would definitely not let it just pass through the earth, nor would it in any other way negate the effects of a black hole. Similarly, the black-holes (perhaps) created in the LHC would probably be moving faster.
Also, a significant amount of high-enery astrophysical phenomena would much more likely create mini-black holes, way more of them, and they would have a more pronounced effect on their surroundings then one would here - making them easier to see (and i'm not talking about the phenomena which we already know to create black-holes).

I can probably come up with some more reasons, but lets leave it at this for now.

First of all, you should remember that it is very unlikely that we can even see black-hole in LHC. All guesses that we can make hint towards too low energy at LHC. I think this should be emphasized in the first place. That we can see them would be a surprise ! (Listen to Lisa Randall lectures in CERN for instance.)

Second, Hawking calculation is not just a "bunch of if and then". There is no way out of Hawking calculation. It has been done like 10 different manners, some of them completely independent and barely remotely connected. Serious.

Third, if you do not want to accept the cosmic ray argument, that means you don't really understand it anyway. It is the same argument as "if string theory is right about producing BH, it must be right about evaporating them". When you are concerned about possibilities at LHC but not about cosmic rays, which are there for million/billion of years and have not destroyed Earth, there is some sort of schyzophrenia somewhere.

Finally let me state firmly : When we make an experiment we have indeed no clue of everything that may happen. That is the beauty of it. If you want to seriously calculate the probability that we destroy Earth, you end up with something ridiculously smaller than many other serious global threats. What is the probability of collision with a massive armagedon ? What is the probability that we all die of a new sort of virus ? What is the probability that we end up in a nuclear global war ? Being concerned about LHC destroying Earth is much worse un-rationality than for instance being concern of taking a plane but walking in the streets of a major city where you can be hit by a car anytime.

In the end, what I think is that there are serious issues of communication somewhere. People talk about BH in LHC, which is completely irrelevant, and forget about the electroweak breaking, which we know we're going to understand, and this is relevant. BH are a remotely exotic possibility within already exotic scenario anyway. And macroscopic BH in LHC is b**ls**t in an exotic version of an exotic scenario. What a shame that so much is spend on internet discussing this.

Ok, first, you don't have to resort to calling me mentally ill. I'm not saying I believe this will happen (some are!). I find the topic fascinating and, like I said, I wish there were more certainty.

Science has caused grave, grave harm to our planet in the past. We burned fossil fules for decades before we had a clue of the long term effects. How many drugs have we found that cause cancer or other problems? Nuclear weapons, if we ever used them at a large scale, would end life as we know it.

It's only a matter of time before our harnessing of the power of nature poses risk not just to the health of the planet but to its very existence. Perhaps we are not there yet; but one day we will be. And therefore it is not unreasonable to question whether we know what we're doing when we start playing with singularities. That's not being alarmist, being a conspiracy theorist, schizophrenic, or anything else except prudent. Asking for the opinions of a few experts in a coffee-room discussion such as this should not generate indignance or anger or namecalling.

Finally, if the cosmic rays that could form a singularity under the same conditions as the LHC actually wouldn't be going fast enough to shoot through the earth harmlessly, that does improve the situation in my view. That was my chief objection to the cosmic ray argument.

Finally, if the cosmic rays that could form a singularity under the same conditions as the LHC actually wouldn't be going fast enough to shoot through the earth harmlessly, that does improve the situation in my view. That was my chief objection to the cosmic ray argument.

What do you call fast enough ?

You have a spectrum of ultra high cosmic rays. This spectrum extends far beyond the LHC reach. Look at Figure 24.1 in PDG review for the number of protons between [tex]10^{5}[/tex] and [tex]10^{6}[/tex] GeV : you have around [tex]10^{-10}[/tex] of them per square meter per steradian per second per GeV. Compare to the LHC parameters in the same review, which tells you that LHC will not reach more than a few TeV. Consider the enormous total surface of the Earth (something like [tex]1.5\times 10^{14}[/tex] square meters), which is here for 5 billion years (something like [tex]10^{17}[/tex] s) and you can see that

the Earth has already received thousands of billions of billions of collisions per steradian per GeV more energetic than the highest reach of the LHC.

Now, please forgive my rudeness, of don't, but how can one have a decent scientific discussion and not be able to make this simple evaluation ? I can even be wrong by several orders of magnitudes, it does not matter. The number above is so incredibly huge, that is thousands of billions for each people living today ! We are not even talking about probabilities anymore at this level. Besides, I only took into account cosmic protons, not even to mention all the other nuclei/particles.

I want to repeat my point. We have a major communication problem. A few physicists decided to talk about the exotic scenario that we see BH in LHC. This is a very nice possibility scientifically, mainly because it would reveal a lot of very fundamental facts, and if it is there it will be very easy to identify. But this is an exotic scenario the public should not focus on. If we discover supersymmetry and no BH, will the public be disappointed ?

Well, since you asked - "fast enough" means the micro black holes, if they _are_ created in the atmosphere, have so much momentum that they would slice right through the earth and out the other side before the earth's gravity would capture them.

The question is whether theoretical MBH's created by cosmic rays would, in fact, be "fast enough." If not, then your argument is sound, because then we would expect anything we create at LHC to be orders of magnitude less energetic.

If, on the other hand, those cosmic-ray MBHs ARE slicing right through the earth and out the other side, then we can't compare them to what we might create at the LHC.

Anyway, I realize that if an MBH were created it would be exotic, but I, for one, am hoping that something exotic IS discovered to hopefully get physics out of the rut it's in now.

Peter, i applaud your question and your general interest; i wish more people shared it.
The LHC will pose virtually no threat to the earth or humanity; it is, however, the door to some of the most amazing physics of our time - and represents the amazing ability of humanity when we think and work together.
Science, research, and learning in general can always be a danger; and always requires a great deal of responsibility to wield. None-the-less, our strive to learn and progress is possibly the most important of all.

If a sustained black hole was created I doubt we would have enough time to realise what was going on anyway =D. I doubt they would be created, small ones should just evaporate according to Hawking radiation. Large black holes are created by stars with density above Chandrasekhar's Limit.

When I see a one-word reply like that, this sounds more like a debate than a dialog. While I am willing to have a dialog, I'm not interested in debating this. There simply aren't two sides.

Now, to make a BH in a collider, you have to change its production properties. Classical BH theory says that the production probability is of order forty orders of magnitude too small to be produced at the LHC. Then, for it to be dangerous, the BH has to be kept from evaporating, so you need to change its decay properties. That's why I argued that one shouldn't use the term BH to describe things like this - their properties are different.

Note that to increase the production cross-section you need to increase the BH's coupling to matter. Note to decrease the Hawking radiation, you need to decrease the BH's coupling to matter. So not only are you ascribing new properties to the BH, you are ascribing mutually contradictory properties.

Next is the kinematics. For a BH to be dangerous, it needs to be moving slower than escape velocity. That's about .00004c. Virtually everything produced at a collider is moving much, much faster than this. Even very heavy objects like top quarks. (I am reasonably certain that there is no reconstructed object produced at the Tevatron in any channel whatsoever that is moving this slowly) This is because it is almost impossible for the two quarks or gluons that collide to carry exactly the same momentum, so the thing that is produced ends up with some motion. This is true for anything produced by the collision of quarks and gluons, so if you want BH's to be produced at rest, you need to find a reason to toss a couple of decades of measurements of particle production.

Finally is the gravitational field. Suppose you had a 4 TeV BH. That would have an event horizon 10^-56 meters across. So the probability of it sucking in even a single atom is tiny. In fact, the mean free path is something like 10^82 meters. Even if one somehow ended up trapped inside the earth, it would take a long time for it to even eat its first atom: around 10^70 years. To make it dangerous, you need to make its gravitational effects bigger. Not just twice as big or a hundred times of big: 30 to 40 orders of magnitude bigger.

I understand the general consensus is that the LHC poses no real threat and that the formation of stable micro-singularities is highly unlikely. My question however is this - if in the off chance the LHC does produce a stable micro-singularity, would it be possible to contain it, and harness or control it?

According to current theory: no. The smaller a black-hole is, the faster it evaporates (see Hawking Radiation). The micro blackholes that might be produced, would exist for only the smallest fraction of a second.